The following invention relates to systems for feeding hydraulic fluid or other compressed propellant powered tools into a workpiece to be cut. More particularly, this invention relates to feed systems which automatically adjust a rate at which a hydraulic fluid powered work head advances into a workpiece in response to a hydraulic pressure in an inlet line feeding hydraulic fluid to the work head of the tool, so that maximum torque thresholds for the work head are not exceeded.
When a workpiece is to be cut with a powered work head, it is important that the work head not cut the workpiece in a manner which exerts more forces on the work head than the maximum forces for which the work head is designed, so that the work head does not experience premature wear. When the workpiece is concrete or other hard materials, the importance of not exceeding these maximum forces is particularly great. Concrete is typically cut with diamond tipped work heads, such as drill bits or saw blades, which are relatively expensive and susceptible to damage when forces experienced at the tip of the work head exceed forces with which the diamonds are bonded to the work head.
Typically, the work head is rotated by an output shaft from a motor, causing the work head, such as the saw blade or drill bit, to rotate relative to the workpiece. The work head can be rotated by a variety of different motors. One motor which is desirable in many workpiece cutting applications is a hydraulic motor which has elevated pressure hydraulic fluid delivered to the work head motor through an inlet line to power the work head motor. When the work head is driven by a hydraulic work head motor, the shearing forces experienced by the work head where it abuts and cuts the workpiece are proportional with torque in the output shaft of the work head motor and pressure in the hydraulic fluid inlet line feeding the work head motor.
Increases in work head torque, and corresponding inlet line pressure increases are related to a feed rate, also called advance rate, and associated feed forces which are exerted on the work head to drive the work head into the workpiece. It is desirable to properly select the feed rate for the work head so that the workpiece can be cut as quickly as possible without exceeding the maximum torque for which the work head cutting surface is designed.
When a workpiece being cut has irregular hardness and exerts variable shearing forces on the work head, advancing the work head at a constant feed rate can lead to periods of excessive torque and shear forces and corresponding excessive wear of the cutting surfaces of the work head. For instance, when concrete is being cut with a diamond tipped saw or drill bit, and the concrete has reinforcing steel therein, the work head will occasionally encounter this steal within the concrete. When the feed rate is manually adjusted by an operator, the all to common tendency is to accelerate the feed rate when obstacles such as rebar are encountered to xe2x80x9cpush throughxe2x80x9d such an obstacle. In fact, to maintain torque and shear forces on the work head below maximum thresholds, a slower feed rate is called for until the reinforcing steel or other obstacles are passed. Accordingly, a need exists for a feed system for a hydraulic fluid powered work head which automatically adjusts the feed rate to keep torque shearing forces on the work head below acceptable threshold values.
With this invention the hydraulic fluid powered work head motor has its feed rate controlled by a feed motor or other advance which variably selects its feed rate depending on a pressure in an inlet line directing hydraulic fluid to the work head motor. Preferably, the feed motor is in the form of a hydraulic motor fed by an elevated pressure hydraulic fluid feed line separate from the inlet line to the work head motor. While the feed rate of this feed motor could be modified and controlled in a variety of ways, in a preferred form of this invention the feed rate of the feed motor is controlled by a pressure sensitive valve diverting at least a portion of hydraulic fluid in the feed line away from the feed motor when the pressure sensitive valve senses an elevated pressure, in the hydraulic fluid inlet line directing hydraulic fluid to the work head motor, which exceeds a preset maximum.
Hence, when the work head motor encounters an obstacle which is causing elevated torque and shearing forces on the work head, and the corresponding hydraulic fluid inlet line pressure increases, this increase in pressure in the inlet line of the work head motor is sensed by the pressure sensitive valve. The valve then causes hydraulic fluid flow through the feed line to the feed motor to be at least partially disrupted, at least partially reducing the feed rate of the feed motor, and hence the advancing forces driving the work head into the workpiece. This decrease in feed rate in turn decreases the shearing forces experienced by the work head. Thus, an automatic control system is provided to advance the work head motor at an optimum speed for efficiently cutting the workpiece and yet avoiding maximum shearing force thresholds when obstacles are encountered which exert increased shearing forces on the work head.
Preferably, the pressure sensitive valve is interposed between a hydraulic power unit supplying elevated pressure hydraulic fluid to the feed motor, and a feed line exiting the valve and extending on to the feed motor. A piston or other movable element within the valve has a first position which allows hydraulic fluid to pass from the hydraulic power unit to the feed motor through the feed line. The piston has a second position where the path from the hydraulic power unit to the feed motor is at least partially diverted. A sensor line preferably extends from the valve to the hydraulic fluid inlet line feeding the work head motor. This sensor line is oriented adjacent the piston so that pressure in the sensor line and the inlet line can cause the piston to move from the first position to the second position. The piston is biased towards the first position and remains in the first position unless the pressure in the inlet line exceeds the biasing force exerted on the piston. This biasing force is preferably adjustable so that a user can selectively set the preset maximum pressure for the inlet line of the work head motor and hence control maximum shearing forces which will be experienced by the work head.
Accordingly, a primary object of the present invention is to provide a system for controlling a feed rate of a work head through a workpiece so that the feed rate does not cause excessive torque and shearing forces to be encountered by the work head.
Another object of the present invention is to provide a feed system which maintains forces on the work head below a maximum threshold to avoid damage to the work head.
Another object of the present invention is to provide a feed system for a hydraulic motor powered work head which varies the feed rate of the work head when hydraulic fluid driving the work head motor increases above a preset maximum, indicating excessive forces on a cutting surface of the work head.
Another object of the present invention is to provide a system for optimizing a speed with which reinforced concrete is cut by automatically adjusting a feed rate of a work head cutting the concrete when reinforcing structures within the concrete are encountered by the work head.
Other further objects of the present invention will become apparent from a careful reading of the included drawing figures, the claims and detailed description of the invention.